Method for bleaching fibrous materials

ABSTRACT

The invention relates to a method for bleaching fibrous materials, in particular lignin-containing materials for producing paper consisting in adding at least a first additive and at least one type of bleaching liquid to a fibrous solution which contains at list one bleaching agent. After mixing said bleaching solution with the fibrous suspension and at the end of determined bleaching time, the bleaching process is ended by adding at least a second additive. Said invention is characterised in that the pH of the fibrous suspension is obtained by adding lime.

The present invention relates to a method and a device for bleachingfibre materials, in particular lignin-containing fibre materials for theproduction of paper.

BACKGROUND OF THE INVENTION

Methods for bleaching fibre materials are known in the state of the art,wherein, in addition to oxidative bleaching means, reductive bleachingmeans are also used in the paper industry for bleaching fibre materials.

In industry, bleaching of lignin-containing fibre materials is carriedout in particular using lignin-preserving bleaching sequences, which arepresently, particularly for reasons of environmental protection,halogen-free bleaching sequences using for example hydrogen peroxide,oxygen or ozone as bleaching means.

For attaining an optimal bleaching result, besides the application of aspecific bleaching means, the process control, in particular the processconditions, is also of decisive significance.

Thus, for example, sodium hydroxide is used in conjunction with theapplication of hydrogen peroxide, which is admixed to the fibre materialin form of caustic soda lye (aqueous sodium hydroxide solution) togetherwith the hydrogen peroxide, or before the hydrogen peroxide is added.

The disadvantages of using caustic soda lye are its relatively high costand the problems associated with its dosage. Thus, in particular a largedeviation of the pH value as a result of using caustic soda lye willlead again to a reduction of the initial degree of whiteness of thefibre material to be bleached.

SUMMARY OF THE INVENTION

It is the object of the present invention to overcome the knowndisadvantages of the prior art at least partially and, in particular, toprovide a cost effective method featuring the use of a cheap lye forbleaching fibre materials for the paper industry.

This object is solved by a method according to claim 1. This object isalso solved by a device according to claim 21, preferred embodiments ofthe invention being the objects of the sub-claims.

According to the present invention, the method for bleaching fibrematerials, in particular of lignin-containing materials for theproduction of paper, includes a plurality of steps, where in at leastone of those steps at least one first additive is dosed into asuspension of fibre material.

According to the present invention, a suspension of fibre material isunderstood to be an aqueous suspension of fibre material containing inparticular natural fibres such as cellulose, waste paper, mechanicalwood pulp and suchlike. Besides the fibre materials, the suspension canhowever also include mineral or other types of components, as is thecase particularly when waste paper is used as heterogeneous rawmaterial.

Besides the addition of the first additive, at least a bleaching lye isdosed to the fibre material, in particular into the suspension of fibrematerial, the bleaching lye including at least one bleaching agent.According to the invention, both the first additive and the bleachinglye are mixed with the suspension of fibre material, the bleachingprocess then finalizing, according to the invention, with the additionof at least one second additive.

According to the present invention, the pH value of the suspension offibre material is adjusted using lime that is, according to aparticularly preferred embodiment of the invention, dispersed at leastpartially in water.

According to the present invention, the pH value adjustment is carriedout by means of the dosed addition of lime in such a manner that eitherthe amount of lime is dosed as a function of a pH value determined inthe suspension of fibre material and/or, according to a particularlypreferred embodiment, the dosage is conducted as a function of theamount of bleaching lye used. However, other dosage forms are alsoimaginable, such as, for example, dosing as a function of the amount offibre material and/or suchlike, which are also understood to be dosingmethods according to the present invention.

According to the present invention, lime is understood to be a substanceincluding at least one component being selected from a group includingcalcium hydroxide, calcium oxide, (calcium) carbonate, fired naturaland/or synthetic minerals, such as, for example, orthoclase, albite,anorthite, kaolinite, mullite, muscovite, calcite, magnesite, artinite,periclase, brucite, dolomite, wollastonite, talc and clinochlore.Furthermore, this group can include further substances, which arepreferably but not exclusively added as impurities and which are, forexample, magnesium (oxide), aluminium silicates/oxides and/or transitionmetal components, in particular iron and manganese oxides/hydroxides,sodium oxide, potassium oxide, silicon oxide, sulfur oxide, as well asbound gaseous components and suchlike.

According to the present invention, mechanical wood pulp is understoodto be, in particular, stone groundwood with and without chemicalpretreatment, refiner mechanical pulp with and without chemicalpretreatment, thermo-mechanical pulp, reground stone groundwood pulp,pressurized stone groundwood, refiner mechanical pulp, pressurizedrefiner mechanical pulp, chemi-groundwood, chemi-refiner mechanicalpulp, chemi-thermo-mechanical pulp and suchlike.

According to a particularly preferred embodiment, the method accordingto the present invention is used for bleaching fibre materials having amaterial density between 5% and 55%, preferably between 10% and 50%,particularly preferably between 15% and 46%. In this context, thematerial density can be between 5% and 20% for so-called lowconsistency, between 20% and 28% for a medium consistency, and between28% and 46% for a so-called high consistency.

According to a further preferred embodiment, the material density isreduced by adding process water and/or fresh water.

According to a further particularly preferred method, the materialdensity of the fibre material is increased mechanically and/or thermallyand/or chemically, that is to say that liquid is removed from thedispersion. In particular, the mechanical increase of the materialdensity is carried out, for example, through the removal of water fromthe suspension of fibre material by means of a twin wire press, a discfilter or suchlike, as they are known in the state of the art.

According to the present invention, the chemical increase of thematerial density is understood to be the addition of dry components,such as lime, which has not been dispersed in water at least partiallyin a preceding dispersion step, but is, instead, dosed into thesuspension of fibre material as a solid, thereby increasing the materialdensity of the suspension of fibre material, that is to say, the solidcontent in relation to a predefined volume.

According to a preferred embodiment, the bleaching lye being dosed intothe suspension of fibre material contains at least one substance withoxidative or reductive effects, causing at least partial bleaching ofthe fibre material, in particular the at least partial destruction ofchromophoric groups, as known in the state of the art. According to aparticularly preferred embodiment, these agents are selected from withina group containing hydrogen peroxide, hypochloride, ozone, oxygen,sodium sulfite, formamidine sulfonic acid, sodium dithionite, sodiumborohydride, peracetic acid, perchloric acid, hydrosulfite, andsuchlike.

It should be noted, however, that in the case of fibres, which are inparticular loaded with impurities with only very weak or no catalyticeffect, the addition of substances such as complexing agents can bedispensed with. The same applies to the use of water glass, such asalkaline silicates and alkaline earth silicates.

According to a particularly preferred embodiment of the presentinvention, the first additive is understood to be an auxiliary meansselected from a group containing water glass, in particular alkalineand/or alkaline earth silicates, complexing agents such as DTPA, EDTAand phosphates and phosphonates, polyhydroxycarboxylic acids, sugarderivates, stabilizers, catalysts, inhibitors and suchlike.

According to a further embodiment of the present invention, agentscomplementing the bleaching lye are used as the second additive,whereby, according to another particularly preferred method, the agentsare selected from a group containing reductive and oxidative agents,such as hydrosulfite, sodium bisulfite, sodium hydrosulfite, sodiumborohydride and suchlike.

According to a preferred executive example, they are used, amongst otherthings, to reduce residues of the bleaching agent previously added bymeans of the bleaching lye as much as possible at the end of thebleaching process, so that its effectiveness for a further subsequenttreatment may not adversely affect the use of further bleaching agents,for example in a second step. According to a particularly preferredembodiment, these can be different bleaching agents, although it is alsopossible to achieve the desired effect in a single step by means of aselective agent.

According to a further particularly preferred method, the lime is storedas a solid and is taken out essentially continuously from a container.Here, essentially continuously is understood to mean a pulsedextraction, as well as a continuous extraction, with and withoutinterruptions, and combinations thereof. The speed of extraction mustalso not be constant, but can instead be regulated and/or controlledaccording to the predefined dosage.

According to a further preferred method, the lime has a solids contentof between 92% and 100%, preferably of between 95% and 99.9%, andparticularly preferably of between 98% and 99.5%.

During the dosage of the lime dissolved and/or dispersed in water, i.e.the dosage of the lime milk into the fibre material suspension, thelatter has a solids content of between 5% and 40%, preferably of between7% and 25 % and particularly preferably of between 10% and 20% andparticularly of less than 17%.

The determination of the solids contents is carried out in accordancewith the regulations set forth by the German Industrial Standard, forexample DIN ISO 787, part 2, or the TAPPI standards known in the stateof the art. The equivalent applies to the determination of furthercharacteristics, which are known in the state of the art as processparameters, quality properties and suchlike within the context of pulpand paper production, and which can be obtained from the DIN or TAPPIstandards.

As already explained, the lime can be also be dosed to the fibrematerial as a solid, whereat, according to a particularly preferredmethod, the lime has a predefined particle size distribution.

The lime dosage can take place before the addition of the first additiveand bleaching lye into the suspension of fibre material, the addition ofthe lime also being possible after the addition of the first additiveand before the addition of the bleaching lye. According to a furtherparticularly preferred embodiment, the lime can also be dosed into thesuspension of fibre material essentially simultaneously with at leastone first additive.

According to the present invention, after the dosage of the lime intothe suspension of fibre material, a pH value in the suspension of fibrematerial ranging between 8 and 12, preferably between 9 and 11 andparticularly preferable between 10.3 and 10.8 is attained.

Furthermore, the amount of lime added in relation to the oven dried(odri) amount of fibre material can be between 0.01% and 5%, preferablybetween 0.1% and 2%, and particularly preferably between 0.3% and 1%. Inaddition, a dosage dependent on the amount of the bleaching means isprovided according to a further executive example, a hydrogen peroxideto lime ratio of between 0.1 and 5, preferably of between 1 and 3 andparticularly preferably between 2.4 and 2.7 being selected.

According to a further particularly preferred executive example, thefibre material is heated by means of steam addition, in particular oflow pressure steam and/or by the introduction of mechanical energy, suchas is the case, for example, when mixing in a high consistency mixer, toa temperature between 40° C. and 100° C., preferably between 45° C. and90° C. and particularly preferably between 60° C. and 70° C.

The addition of the second additive can take place, according to afurther preferred method, after the dilution of the fibre material,being given that sufficient mixing must be ensured in this case as well.

According to a further preferred executive example, process water isused for the dilution of the fibre material, process water beingunderstood to be production water created within the area of fibrematerial bleaching, paper production or equivalent process stages.

According to another particularly preferred embodiment of the method forbleaching fibre materials, a complexing agent is dosed to the fibrematerial, in particular into the suspension of fibre material, thecomplexing agent particularly reducing the catalytic effect of metalssuch as transition metals, in particular metal ions, on thedecomposition of at least one bleaching agent.Diethylenetriaminepentaacetic acid (DTPA), ethylenediaminetetraaceticacid (EDTA), phosphates, phosphonates, polycarboxylic acids, sugarderivates, polyhydroxycarboxylic acids and suchlike can for example beused as complexing agents.

The object is also solved by a device for bleaching fibre materials,including at least one mixer and one reaction space, in which theaqueous suspension of fibre material is subjected to at least onebleaching, in particular bleaching stage, according to predefinedconditions.

This device is further characterized in that a dosing device, whichregulates and/or controls the addition of lime, in particular a lime atleast partially dispersed in water, into the aqueous suspension of fibrematerial as a function of predefined process parameters is provided.

According to a particularly preferred embodiment of the device accordingto the invention, the process parameters are selected from a group ofparameters containing the pH value, the amount of bleaching agent, theamount of bleaching lye, the brightening, the degree of whiteness, thechromaticity coordinate, the reaction time, the bleaching temperature,the content of residual bleaching means, the amount of fibre material,the solids content, the material density, the pressure, the mixing andsuchlike.

According to another preferred executive example of the device, the limeis taken out essentially continuously from a storage container,preferably as a solid, and diluted with water to a predefined solidscontent before being added into the suspension of fibre material. Inparticular fresh water such as well and/or surface water and/or processwater can be used as possible diluting water.

The object is further solved by a device for bleaching fibre materials,including at least a first container for storing lime having apredefined particle size distribution and purity, an extracting deviceand a transport and/or mixing device, in which the lime is dissolvedand/or dispersed, and further including at least a second container, towhich the lime is transported and in which the latter is mixed with asuspension of fibre material according to predefined process parameters.

Further explanations are provided hereinafter with reference to thefigures and the executive example. The results shown here shall howevernot limit the scope of the invention and merely represent executiveexamples aimed in particular at the application of the system forbleaching mechanical wood pulp. It is however also possible within themeaning of the present invention to use the present method or,alternatively the device according to the present invention, for otherfibre materials, as was explained earlier.

Accordingly:

FIG. 1 shows a flow diagram for the implementation of the method forbleaching fibre materials according to the invention.

FIG. 1 represents a schematic flow diagram for the implementation of themethod for bleaching lignin-containing mechanical wood pulps, such asthose used for example for the manufacture of stone groundwood for theproduction of paper, in particular mass-print papers.

Before the actual bleaching, the fibre material is taken out from astorage container 1, the so-called storage tower, the transport beingfacilitated by diluting the wood pulp through the addition of processwater 20, for example filtrate, and feeding it to a mechanicalthickening device 2 by means of a feed system.

The thickening device 2 can be, for example, a twin wire press, whichincreases the material density of the mechanical wood pulp to a range ofbetween 25% and 28% solids content.

Other water removal techniques known in the state of the art are howeveralso possible.

According to a particularly preferred embodiment, the fibre material canalready have a first additive, such as a complexing agent, dosed to itin the storage container, at its outlet, or in the transport device, thedosing amount being dependent in particular on the loading of the fibrematerial or dilution water with possibly catalytically acting metals, inparticular metal ions. According to the executive example presentedhere, 0.3% of DTPA per 9 t of wood pulp are added to the wood pulp.

The thickened fibre material is transported from the twin wire press 2over a feed screw 3 and a transport device to a mixing device 4.

According to the embodiment presented here, the lime is dosed to thefibre material already at the feed screw 3, the feed screw 3, inparticular, being used for mixing of the fibre material with the limemilk. The fibre material is subsequently shredded, loosened andtransported. It is, however, also compatible with the meaning of thepresent invention to place the dosing location in another position, inparticular when the reaction time and the mixing are adapted to thepredefined conditions.

To ensure sufficient mixing and homogenization of the fibre material,according to a particularly preferred embodiment, an exposure time isselected between the addition of the lime milk and the following dosageof further additives or bleaching agents, depending on the position ofthe dosing location and taking into consideration the flow conditions.

According to the executive example presented here, the exposure time ispreferably between 10 and 60 seconds.

The mixing of the fibre material after the dosed addition of a furtheradditive, for example an alkaline or alkaline earth silicate, and thedosed addition of the bleaching lye, in particular of the bleachingagent, takes place according to the method presented here by means of ahigh consistency mixer 4. The material density is between 18% and 35%,being given that, according to the executive example presented here, aso-called high consistency mixer (Kamyr mixer), as known in the state ofthe art, is used. Other mixing devices can, however, be used as well,such as, particularly, but not exclusively, a double shaft mixer,particularly when the material density of the fibre material is adjustedwithin the low and medium concentration range.

Subsequent to the mixer, the fibre material is conveyed by means of atransport device, such as, for example, a feed screw 5 for a materialdensity >20%, into a reaction space 6 such as, for example, a bleachingtower.

It should be noted, however, that the tests were carried out at theabove-mentioned material density. It is however explicitly within themeaning of the present invention not to limit the material density tothis value for the implementation of the method, but rather to considera wide range of adjustment for the material density of the fibrematerial.

According to the executive example presented here, the fibre material isheated to a predefined temperature by supplying mechanical energy in thehigh consistency mixer and/or through the addition of low pressuresteam. According to the executive example presented here, thistemperature lies in the range between 55° C. and 70° C., although itshould be noted that exceeding a temperature of 80° C. is detrimental,particularly when using alkaline and/or alkaline earth silicates,because at this temperature a precipitation of the additives can alreadytake place, e.g. through the formation of quartz sand.

It should further be noted that observance of the above-mentionedtemperature limits for the bleaching process is not required when theuse of such auxiliary means is dispensed with, so that the temperaturespredefined by the system can be used in full and, for example, exceed90° C.

To ensure that sufficient time is available for the bleaching agent toreact with the fibre material, in particular with the chromophoricgroups of the fibre material, the residence time of the fibre materialwith the added bleaching agent and lime milk inside the bleaching toweris 30 to 180 minutes, with the reaction time being determined inparticular as a function of the desired degree of whiteness and/orresidual content of bleaching agent in the fibre material.

According to the executive example presented here, the reaction time isbetween 60 minutes and 3 hours for a material density of approximately20% to 27% and a temperature of between 60° C. and 70° C. The pH valuein the initial stage is approximately 10.8% to 11.2% and falls to avalue of between 6.3% and 7.3% in the course of the bleaching stage.

According to the executive example presented here, the fibre material isdiluted with process water 24 after an extracting location, the materialdensity then being between 2 and 5% according to the executive examplepresented here.

It should further be noted that, before and/or after the dilution withprocess water, a second additive is added to the fibre material takenout from the bleaching tower 6, which, according to the executiveexample presented here, reduces the amount of residual bleaching agentpossibly still present within the fibre material in such manner as toconclude the bleaching stage.

This fibre material is fed by means of a transport device to a furthermechanical water removal device 7—e.g. a twin wire press—, in which thematerial density is increased to a range of between 18% and 35%,particularly to 26%.

The fibre material is accumulated in the feed screw according to theexample presented here and fed into a storage vat 9.

According to a particularly preferred executive example, the fibrematerial has its degree of whiteness further increased and/or itschromaticity coordinate changed in a subsequent second stage by means ofthe application of a further, in particular reductive bleaching agent.This bleaching can again take place, for example, in a reactioncontainer, e.g. a bleaching tower 10, with the reaction time essentiallyhere also depending on the agent used. The then completely bleachedmechanical wood pulp is intermediately stored in a so-called storage vat11 for processing in the production of paper 12.

APPLICATION EXAMPLE

The executive example shown hereinafter illustrates four practicalbleaching tests using mechanical wood pulp which was bleached with themethod according to the present invention.

Here, the three tests differentiate themselves amongst other things inthe amount of active bleaching agent used, here hydrogen peroxide(H₂O₂), and in the amount of added lime or water glass. The exactamounts used can be obtained from Table 1: Amounts used. TABLE 1 Amountsused Test 1 Test 2 Test 3 Test 4 H₂O₂ [50%] 3.0% 6.0% 7.4% 3.0% Lime[17%] 2.2% 3.4% 3.8% 2.2% Water glass 0.9% 2.2% 3.0% 0.9% Mixing unitHigh Double High High consistency shaft consistency consistency mixermixer mixer mixer Material density  26% 20-25%  26% ˜17.5% Temperature65° C. ˜55° C. 65° C. 65° C.

A high consistency mixer (Kamyr mixer) was used as the mixing unit intest series 1, 3 and 4 and a double shaft mixer was used as the mixingunit in test series 2.

The material density in test series 1 and 2 was 26%, in test series 2 itwas 20 to 25%, and in test series 4 it was approximately 17.5%. Thereaction temperature was set at 65° C. for test 1 and was atapproximately 55° C. for test 2.

While performing these tests, quick lime (calcium hydroxide; Ca(OH)2)with a certain fraction of impurities was used as lime or lime milk. Thelime was stored in a silo as a solid and diluted to a solids content ofapproximately 17% with fresh water by means of an extracting device anda dispersion device connected thereto.

The bulk density of the lime was 0.5 g/cm³, (EP 459-2), with the sieveanalysis according to EP 459-2 resulting in a 0.0% residue for a 0.2 mmsieve and a 2.1% residue for a 0.09 sieve.

The amounts used according to the formulation relate explicitly to theamount of oven dried wood pulp introduced. The process controlcorresponds to the flow diagram represented in FIG. 1.

The test results can be obtained from Table 2. TABLE 2 Measured valuesTest 1 Test 2 Test 3 Test 4 Initial whiteness ˜62 ˜62 ˜62 ˜62 (R457)Final whiteness ˜74 ˜76.5 ˜78.5 ˜74 (R457) COD value <1700 ˜2500 <1700˜1650 Residual peroxide 20-300 300-600 20-300  20-150 20-150 CaO value150-250  150-300 25-400 150-250

(Percentages Refer to Odri Fibre Material) Comparative values when usingNaOH: Hydrogen peroxide (H₂O₂) [50%]: 7.4 NaOH [50%]: 4.0 Water glass:1.7 Residual peroxide: 90-800 or 200-350 CaO value: 85-120 COD value:Bleaching tower 1B > 2800; Bleaching tower 1A 4000-5000

Apart from the final whiteness obtained, the measured COD values,residual peroxide contents and calcium oxide values are particularlynotable.

Compared to the results obtained when using caustic soda lye, the CODvalue of <1700 falls clearly below the value obtained with theapplication of caustic soda lye. In practical tests, this tendency alsoaffected the COD load in the inlet and outlet of the final clarificationof the wastewater treatment plant connected to the factory. Here, theCOD load in the inlet was reduced by about 15% for full capacityoperation of a bleaching line. A COD reduction of 25% is realistic ifall the bleaching lines are operated with lime milk.

The residual peroxide content, which expresses the bleaching effect ofthe peroxide on the fibre material, was clearly lower compared to theresults obtained when using caustic soda lye, with the determined valueslying between 20 and 300 or between 20 and 150. The measurement tookplace in the individual fibre material filtrate prior to the dilutionpreceding the bleaching in the reaction space.

Solely the value for the amount of calcium oxide in the bleached fibrematerial increased slightly when using lime milk in comparison to theapplication of caustic soda lye, with the values in the range of 150 to250 being within the process tolerance limits.

It should further be noted that, on the basis of practical tests and theassociated quality criteria for the application of the bleachedmechanical wood pulp in production, the degree of whiteness in tests 1and 2 was used as control quantity for the application of hydrogenperoxide.

In addition to the above-mentioned test results it should further berecorded that with the application of the so-called “lime milk” a morestable bleaching process, which is also reflected by a more stabledegree of whiteness was achieved. This way, the fluctuations relating tothe application of caustic soda lye were typically between 2 and 5degrees of whiteness, while for the application of lime milk thefluctuations were at <1.5 degrees of whiteness. Generally, the tolerancefor dosing errors was noteworthy with lime milk. Among other things, anoverdosing of 20% lime milk did essentially not have a negativeinfluence on the final whiteness.

Temporary increases of the degree of whiteness above average were alsoregistered with the application of lime milk.

The use of lime as a bleaching agent is also interesting from aneconomical point of view. Thus, the price level for slaked lime as aproduct for processing a raw material available in nature is well belowthat of caustic soda lye, which is produced in a complex process bymeans of chlor-alkali electrolysis. Furthermore, it is much lessvolatile. In addition, it should be noted that the actual requiredamount of bleaching agent can be partly noticeably reduced.

1. Method for bleaching fibre materials, in particular lignin-containingfibre materials for the production of paper, including the steps ofadding at least one first additive into a suspension of fibre material;adding at least one bleaching lye into the suspension of fibre material,the bleaching lye having at least one bleaching agent; mixing thebleaching lye with the suspension of fibre material; completing thebleaching process with the addition of at least one second additive,characterized in that lime is used at least for adjusting the pH valueof the suspension of fibre material before the bleaching.
 2. The methodaccording to claim 1, characterized in that the lime is dispersed atleast partially in water.
 3. The method according to claim 1,characterized in that the lime has at least one component selected froma group consisting of calcium hydroxide, calcium oxide, carbonates,natural and fired natural minerals such as, for example, orthoclase,albite, anorthite, kaolinite, mullite, muscovite, calcite, magnesite,artinite, periclase, brucite, dolomite, wollastonite, talc, clinochloreand accompanying substances such as, for example, magnesium oxide,aluminium oxide, iron oxide, sodium oxide, potassium oxide, siliconoxide, sulfur oxide, as well as bound gaseous components and suchlike.4. The method according claim 1, characterized in that the fibrematerial is selected from a group of fibre materials containing naturalfibre materials such as cellulose, waste paper, mechanical wood pulp, inparticular stone groundwood (SGW) with and without chemicalpretreatment, refiner mechanical pulp with and without chemicalpretreatment, thermo-mechanical pulp (TMP), reground stone groundwoodpulp (RSGW), pressurized stone groundwood (PGW), refiner mechanical pulp(RMP), pressurized refiner mechanical pulp (PRMP), chemi-groundwood(CGW), chemi-refiner mechanical pulp (CRMP), chemi-thermo-mechanicalpulp (CTMP) and suchlike.
 5. The method according to claim 1,characterized in that the material density of the suspension of fibrematerial is between 5% and 55% preferably between 10% and 50%,particularly preferably between 15% and 46% and particularly between 5%und 20% for low consistency, between 20% and 28% for medium consistencyand between 28% and 46% for high consistency.
 6. The method according toclaim 1, characterized in that the bleaching lye contains at least onebleaching agent from a group of bleaching agents which cause oxidativeor reductive bleaching, in particular from the group of hydrogenperoxide, hypochloride, ozone, oxygen, sodium sulfite, formamidinesulfonic acid, sodium dithionite, hydrosulfite and suchlike.
 7. Themethod according to claim 1, characterized in that the first additive isselected from a group of auxiliary means containing water glass, inparticular alkaline and/or alkaline earth silicates, complexing agentssuch as, for example, DTPA, EDTA and phosphates, stabilizers, catalysts,inhibitors and suchlike.
 8. The method according to claim 1,characterized in that the second additive is a complementary agent tothe bleaching lye.
 9. The method according to claim 1, characterized inthat the second additive is selected from a group containing reductiveand oxidative agents such as, for example, hydrosulfite, sodiumbisulfite, sodium hydrosulfite, sodium borohydride and suchlike.
 10. Themethod according to claim 1, characterized in that the lime is taken outas a solid essentially continuously from a container.
 11. The methodaccording to claim 10, characterized in that the lime with a solidscontent of between 92% and 100%, preferably between 95% and 99.9% andparticularly preferably between 98% and 99.5% is stored.
 12. The methodaccording to claim 2, characterized in that the aqueous dissolved and/ordispersed lime has a solids content of between 5% and 30%, preferably ofbetween 7% and 25%, particularly preferably of between 15% and 20% andparticularly of approximately 17% odri.
 13. The method according toclaim 1, characterized in that the lime is dosed into the suspension offibre material before the addition of the first additive and thebleaching lye.
 14. The method according to claim 1, characterized inthat the lime is dosed into the suspension of fibre material after thefirst additive and before the addition of the bleaching lye.
 15. Themethod according to claim 1, characterized in that the lime is dosedinto the suspension of fibre material essentially simultaneously with atleast the first additive.
 16. The method according to claim 1,characterized in that the pH value of the suspension of fibre materialafter the addition of the dissolved and/or dispersed lime is between 8and 12, preferably between 9 and 11 and particularly preferable between10.3 and 10.8.
 17. The method according to claim 1, characterized inthat the amount of lime added is between 0.01% and 5%, preferablybetween 0.1% and 2%, and particularly preferably between 0.3% and 1% inrelation to the odri (oven dried) amount of fibre material.
 18. Themethod according to claim 1, characterized in that the fibre material isheated by means of steam addition, in particular of low pressure steamand/or by means of mechanical energy during the mixing, to a temperaturebetween 50° C. and 100° C., preferably between 55° C. and 90° C. andparticularly preferably between 60° C. and 70° C.
 19. The methodaccording to claim 1, characterized in that the fibre material isdiluted before the addition of the second additive.
 20. The methodaccording to claim 1, characterized in that before the bleaching processthe catalytic effect of available metals, in particular available metalions, on the decomposition of at least one bleaching agent is reduced atleast partially by means of the addition of at least one complexingagent such as, for example, diethylenetriaminepentaacetic acid (DTPA),ethylenediaminetetraacetic acid (EDTA), phosphates, polycarboxylic acidsand suchlike.
 21. A device for bleaching fibre materials with at leastone mixer and one reaction space in which an aqueous suspension of fibrematerial is subjected to at least one bleaching, in particular onebleaching stage, characterized in that a dosing device, which regulatesand/or controls the addition of lime, in particular a lime at leastpartially dispersed in water, into the aqueous suspension of fibrematerial in the bleaching process as a function of predefined processparameters is provided.
 22. The device according to claim 21,characterized in that the process parameters are selected from a groupof parameters containing the pH value, the amount of bleaching agent,the amount of bleaching lye, the brightening, the degree of whiteness,the chromaticity coordinate, the reaction time, the material density,the pressure, the mixing, the temperature, the content of residualbleaching means and suchlike.
 23. The device according to claim 21,characterized in that the lime is taken out as a solid essentiallycontinuously from a storage container and diluted with water to apredefined solids content before being added into the suspension offibre material.
 24. A device for bleaching fibre materials with at leasta first container for storing lime having a predefined particle sizedistribution and purity, an extracting device and a transport and mixingdevice in which the lime is dissolved and/or dispersed and transportedto at least a second container, and in which the at least partiallydispersed lime is mixed with a suspension of fibre material according topredefined process parameters.